Broad band radio frequency transformer



Feb. 21, 1967 J. H. TOOMBS BROAD BAND RADIO FREQUENCY TRANSFORMER Filed March 25, 1965 FIG. I

INVENTOR, JOHN H TOOMBS.

ATTORNEYS United States Patent Office 3,305,811 BROAD BAND RADIO FREQUENCY TRANSFORMER John H. Toombs, Rochester, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Mar. 25, 1965, Ser. No. 442,833 8 Claims. (Cl. 336-83) The present invention relates to a novel and useful transformer and more particularly to a ferrite-cored transformer which is useful over a wide range of radio frequencies.

Prior art transformers of this type were not capable of covering the entire frequency range of 2-30 me. with an acceptable voltage standing wave ratio (VSWR) because of lack of constant permeability and coupling over the frequency range. The result was that a plurality of transformers had to be used in some applications or a high VSWR had to be tolerated.

It is an object of the present invention to overcome these disadvantages of prior transformer design to provide an RF transformer with a VSWR of less than 2 over a wide range of RF frequencies.

Another object of the invention is to provide an improved wide-band transformer.

Briefly stated these objects are attained by providing a transformer comprising a plurality of hollow tubular core elements arranged in a closed loop, with the windings thereof threaded through the hollow core elements. Different core elements are composed of different types of ferrite having different permeabilities so that the composite permeability and coupling remain substantially constant over the frequency range of interest. This design also minimizes magnetic leakage.

These and other objects and advantages of the invention will become apparent from the following detailed description and drawing, in which- FIG. 1 is an isometric view of a transformer which illustrates the present invention, and

FIG. 2 shows the complete transformer package after potting.

in FIG. 1 the cylindrical tubular core elements 4, 5, 6 and 7 are all the same size and shape and are all attached to insulated base plate 8 to form a square core. The ends of each core element are beveled at 45, as shown at 3, from a point approximately at the longitudinal center line or the cylinder axis, to the periphery. This arrangement provides good mechanical and magnetic contact where the beveled elements are joined and also leaves openings 15 at each corner of the core, through which the transformer windings may be threaded or fed during manufacture. Part of core element 7 is shown broken away to illustrate the position of the windings relative to the core. The windings lie in a loop within the core as illustrated by winding 14. The end of the windings are attached to terminal posts, 9, 10, 12 and 13, which are mounted on base plate 8.

In accordance with one feature of the invention, the ferrite core elements are composed of different type ferrites. For example, in one transformer constructed according to this invention, two of the core elements were composed of E type ferrite with an initial permeability of 15:20%, one core element of D type fer-rite with initial permeability of 50:20% and the other core element of C type ferrite with initial permeability of :20%. By using these three types of ferrite in a core arrangement of this type, a relatively constant value of permeability and a relatively high coupling coefficient is obtained over the frequency range of 2 to 30 mo, with a VSWR of less than 2.

FIG. 2 shows the transformer potted or embedded in polyurethane foam of low dielectric constant, which seals it against humidity, fungus and mechanical shock. The terminal posts 9-13 extend through the potting material so that the transformer package can be plugged into a circuit board.

While the ferrite tubes have been shown as beveled cylinders, tubes of square or oblong cross-section can also be used. Also, the number of core elements need not be four, a greater or lesser number may be used and arranged in a loop to form a polygon.

While the invention has been described in connection with an illustrative embodiment, the inventive concept disclosed herein may take other forms which will be obvious to those skilled in the art. Hence, the invention should be limited only by the scope of the appended claims.

What is claimed is:

1. A broad band radio frequency transformer comprising a plurality of hollow tubular ferrite core elements arranged in end-to-end relation to form a closed loop, the ends of each said core element being beveled from the approximate longitudinal center line thereof to the periphery thereof, and a plurality of windings threaded through the interior of said core elements.

2. The transformer of claim 1 wherein different core elements are composed of different types of ferrite.

3. The transformer of claim 1 wherein said plurality of core elements is four, one pair of which have the same permeability and the other pair have permeabilities different from each other and different from the permeability of said one pair.

4. A wide band radio frequency transformer comprising a plurality of hollow ferrite core elements arranged end to-end to form a closed loop with one or more windings threaded through the cavity formed by said plurality of core elements.

5. The transformer of claim 4 in which the plurality of said core elements is four, one pair of which have the same permeability and the other pair have permeabilities different from each other and different from the permeability of said one pair.

6. A radio frequency transformer comprising four hollow tubes of ferrite, the ends of each tube being beveled from the approximate longitudinal center line thereof to the periphery thereof so that the beveled surfaces form an angle of 45 with said longitudinal center line, said tubes being arranged in a square configuration with said beveled surfaces abutting, and a plurality of windings threaded through the cavity formed by the hollow interior of said four tubes.

7. The transformer of claim 6 in which one pair of said tubes have the same permeability, and the other pair of said tubes have permeabilities different from each other and different from the permeability of said one pair.

8. A radio frequency transformer comprising four hollow cylindrical tubes of ferrite, the ends of each said tube Patented Feb. 21, 1967 I being beveled from the approximate longitudinal center line thereof to the periphery thereof so that the beveled surface form an angle of 45 with said longitudinal center line, said tubes being arranged in a square configuration and mounted on a fiat, insulated base plate with said beveled surfaces abutting, a plurality of windings threaded through the cavity formed by the hollow interior of said four tubes, the ends of said windings being connected to terminal posts mounted on said plate.

References Cited by the Examiner UNITED STATES PATENTS 1/1956 Gould et al 336-96 11/1960 Gellert et a1 336-96 X LEWIS H. MYERS, Primary Examiner.

T. J. KOZMA, Assistant Examiner. 

4. A WIDE BAND RADIO FREQUENCY TRANSFORMER COMPRISING A PLURALITY OF HOLLOW FERRITE CORE ELEMENTS ARRANGED END-TO-END TO FORM A CLOSED LOOP WITH ONE OR MORE WINDINGS THREADED THROUGH THE CAVITY FORMED BY SAID PLURALITY OF CORE ELEMENTS. 